function Map (el){
    // 保存地图
    this.el = el
    // 记录地图相关属性
    this.width=800
    this.height=400
}

Map.prototype.create = function(){
    // 设置地图宽高\背景\边框
    this.el.style.width = this.width+'px'
    this.el.style.height = this.height+'px'
    this.el.style.background = 'url(./bg.png)'
    this.el.style.border='10px solid green'
    this.el.style.position='relative'

}